Photographic reversal process and bleach bath for use therein



PATENT OFFICE PHOTOGRAPHIC REVERSAL PROCESS AND BLEACH BATH FOR USE THEREIN Kenneth C. D. Hickman, Rochester, N. Y., as-

signor to Eastman Kodak Company, Rochester, N. Y., a corporation ef New York No Drawing. Application October 9, 1930, Serial No. 487,501

19 Claims.

' It relates specifically to the bleach bath used with that process.

Such a reversal process is customarily used for the development of amateur motion picture film. After exposure, developing, and rinsing, the film is submitted to a reversing or bleaching bath, which preferably contains potassium permanganate. means for making the action of this bleaching bath more uniform, dependable, and satisfactory, and for increasing the life of the bleaching bath.

For the sake of clearness, a formula for the type of bleach under consideration follows:

- Parts Potassium permanganate (4% solution) 1 Sulphuric acid (20%) 1 Water 20 ..Such a bleaching bath, or in fact any bleaching bath containing potassium permanganate, or an oxidizing manganese compound, has a tendency to precipitate manganese dioxide in the film which appearsas a stain having a metallic sheen, and this action results in tanning the gelatin whicli' slows up the bleaching and results in more rapid deterioration of the bath.

..It is well known that manganous salts are liberated in the early stages of the reaction, and that these then react with the unchanged permanganate to precipitate manganese dioxide. As the manganese dioxide begins to be precipitated, the gelatin contracts and hardens. The hardening of the gelatin then further favors the deposition of the dioxide. ,As a result, the upper layers of the gelatin become relatively impermeable and resist the penetration of more bleaching material.

From a study of the chemistry involved, I have been led to believe that there is formed an intermediate product which is a salt or oxide of tri valent manganese, and it is this material, possibly because of its similarity to chromic and aluminum hydrates, which is responsible for hardening the gelatin. Any substance which forms a littleionized complex with the tri-valent manganese ion should relieve the staining and tanning trouble.

In this connection, I have found that the addition of a certain class of substances is useful. The substances which I use are on the one hand the soluble fluorides and their complex salts, and on the other hand the polybasic inorganic acids or their salts, acids in which the second, third, or higher, hydrogen ions are not normally liberated. Of these substances, the soluble fluorides, double fluorides, and the complex salts, flue-silicates and fluo-aluminates, and phosphoric acid and arsenic My invention relates to a method and.

acid are especially useful. They cause a great improvement in the photographic action of the bleach bath, which remains clear and deposits very little sludge or stain.

The action of the bleach bath becomes more dependable, as the bath does not deteriorate so rapidly, and the gelatin is not tanned, which also results in more dependable action. This action I believe is due to the fact that these substances combine with the first reduction products of the permanganate which cause the trouble and convert them into a practically unionized complex containing the tri-valent manganese ions.

I may use the substances, mentioned either in the form of the free acids, in the case of the polybasic acids, or in the form of soluble salts,

with free mineralacid in the bleach. When the salts are used with a mineral acid, as is necessary, there is present in the bath the corresponding free inorganic polybasic acid. In the case of the acids, the amount to be used in the bleach bath is of the order of l to 2 per cent. Thus a suitable formula would be:

Example I Parts Potassium permanganate (4% solution) 5 Sulphuric acid (20%) 5 Phosphoric acid 2 Water";

More of these substances may be used, but in that case care must be exercised, as there appears to be an intermediate range where other bad effects appear. Thus in the case of phosphoric acid, less than 2% or more than 8% must be used. It will normally be satisfactory to use from 1 to 2% of the polybasic acids or their salts in the bleach bath.

In the case of the fluorides or their complex salts, the amount to, be used in the bleach bath is of the order of 2 grams per liter. These substances, such as the fluorides, fluosilicates, or fluo-aluminates of sodium or potassium, have a low solubility but usually more than 2 grams per liter will be dissolved. They should not, however, be used in a much greater concentration than 2 grams per liter. A suitable formula is:

Example II Potassium permanganate (4% solution 50' cc. Sulphuric acid (20%) 50 cc. Sodium fluo-silicate (NazSiFs) L 2 grams Water to 1 liter In place of sulphuric acid other mineral acids may be used and particularly phosphoric acid. When this alone is used no additional substance is required.

I consider as included within myinvention all modifications and equivalents coming within the scope of the appended claims.

What I claim is:

1. The method of avoiding the harmful tanning and precipitating action of a permanganate photographic bleaching bath that consists in adding thereto a polybasic inorganic acid other than sulfuric acid which is capable of forming with manganese a complex salt which is relatively unionized.

'2. The method of avoiding the harmful tanning and precipitating action of a permanganate photographic bleaching oath that consists in adding thereto a salt of an inorganic acid having fluorine as one of its substituents.

3. The method of avoiding the harmful tanning and precipitating action of a permanganate photographic bleaching bath that consists in adding thereto a salt of a polybasic inorganic acid capable of forming with manganese a complex salt which is relatively unionized.

4. A photographic bleaching bath resulting from the aqueous solution of an oxidizing salt of manganese and the salt of an inorganic acid having fluorine as one of its substituents.

5. A photographic bleaching bath resulting from the aqueous solution of potassium permanganate, a mineral acid, and a salt of an inorganic acid having fluorine as one of its substituents.

6. A photographic bleaching bath comprising potassium permanganate, a mineral acid, and a fluosilicate.

7. A photographic bleaching bath comprising potassium permanganate, sulphuric acid and a fiuosilicate.

8. A photographic bleaching bath comprising an aqueous solution of a permanganate, and an agent which substantially prevents the precipitation of manganese dioxide, said agent being se lected from the group which consists of polybasic inorganic acids, other than sulfuric acid, the second, third or higher hydrogen ions of which are liberated to a less degree than the first hydrogen ion, said acids being those capable of forming relatively unionized complexes with manganese salts of those acids and simple and complex salts of hydrofluoric acid.

9. A photographic bleaching bath comprising an aqueous solution of a permanganate, an acid stable in permanganate, and. an agent which substantially prevents the precipitation of man-.

relatively unionized complexes with manganese and salts of those acids.

10. A photographic bleaching bath comprising an aqueous solution of a permanganate, an acid stable in permanganate, and an agent which substantially prevents the precipitation of manganese dioxide, said agent being selected from the group which consists of phosphoric acid and the salts of phosphoric acid.

11. A photographic bleaching bath comprising an aqueous solution of a permanganate, an acid stable in permanganate, and an agent which substantially prevents the precipitation of manganese dioxide, said agent being selected from the group which consists of the polybasic inorganic acids, other than sulfuric acid, the second, third or higher hydrogen ions of which are liberated to a less degree than the first hydrogen ion, said acids being those capable of forming relatively unionized complexes with manganese.

12. A photographic bleaching bath comprising an aqueous solution of a permanganate, an acid stable in permanganate and phosphoric acid.

13. A photographic bleaching bath comprising an aqueous solution of potassium permanganate, sulfuric acid, and phosphoric acid.

14. A photographic bleaching bath comprising a. solution containing parts by weight of a 4% aqueous solution of potassium permanganate, 5 parts of a 20% aqueous solution of sulfuric acid, 2 parts of phosphoric acid, and 100 parts of water.

15. A photographic bleaching bath comprising an aqueous solution of a permanganate and a polybasic inorganic acid, other than sulfuric acid, the second, third or higher hydrogen ions of which are liberated to a less degree than the first hydrogen ion, said acid being capable of forming relatively unionized complexes with manganese. v

16. A photographic bleaching bath comprising an aqueous solution of a permanganate and phosphoric acid.

17. A photographic bleaching bath comprising an aqueous solution of a mineral acid and a salt of a polybasic inorganic acid other than .sulfuric acid, the second, third, or higher hydrogen ions of which are liberated to a less degree than the first hydrogen ion, said acid being capable of forming relatively unionized complexes with manganese.

18. A photographic bleaching bath comprising an aqueous solution of a permanganate, an acid stable in permanganate and a phosphate.

19. A photographic bleaching bath comprising an aqueous solution of a permanganate, sulfuric acid, and a phosphate.

KENNETH C. D. HICKMAN. 

